General Features of a Digital Tablet
Digital tablets are well known, but it will be helpful to review the features and terminology that particularly apply to this invention. The user of a digital tablet positions a device called a "pen" on the tablet surface, and circuits of the tablet provide a pen position signal to an associated data processor. The tablet provides a series of position samples when the user moves the pen across the surface or while the user holds the pen in a fixed position.
The pen signal is an analog signal--the pen coordinates are represented by the amplitude of the pen signal. In the specific tablet that will be described, the pen signals are current analogues that are converted to voltage analogues. The tablet circuits digitize the analog pen position signals and send the digital coordinates to the computer.
It is a general object in this art to provide good resolution at a high sampling rate. Noise in the signal is a principal limitation to resolution and sampling rate, as will be discussed later.